Two students are separated by a 7 m partition wall in a room 10 m high . If both light and sound waves can bend round corners, how is it that the student are unable to see each other even through they can converse easily

Question

$\begin{array}{1 1} \text{Sound waves can bend round the portion , where as the light waves almost go unbent } \\ \text{the size of the obstacle should be compound to the wave length } \\ \text{The angle made by the light waves is almost } 0^{\circ}\\ \text{All of the above} \end{array} $